This invention relates to a device for opening and closing hopper gates of an automatic weighing apparatus and a driving unit for operating such a device.
Automatic weighing apparatus such as combinational weighing systems make use of various combinations of hoppers of both single-gated and double-gated kinds as disclosed, for example, in U.S. Pat. Nos. 4,570,727, 4,678,047 and 4,708,215 assigned to the present assignee. Mechanisms for opening and closing hopper gates tend to be bulky and produce much noise. U.S. Pat. No. 4,705,125 issued Nov. 10, 1987 to Yamada et al. and assigned to the present assignee discloses a relatively compact gate operating system for a combinational weighing apparatus. This prior art device is characterized, on the one hand, as using stepping motors for opening and closing hopper gates such that it is possible, for example, to slow down the motion of a gate immediately before it completely closes and hence the noise of the closing gate can be reduced. On the other hand, however, a rotary disk is attached to the shaft of the stepping motor and gate-operating cams are affixed on both sides of this rotary disk according to this patent such that the linking mechanisms for two gates are operated by the clockwise and counter-clockwise rotations of the stepping motor. With a hopper gate-operating device thus structured, the hopper gates are opened and closed only indirectly and a relatively large number of parts are required for the mechanism. Moreover, there are problem of precision in the production of the cams and adjustment of the stepping motor because of the complicated control of its rotation.